distance between backs of wheel flanges

例句：

1. 1.The distance between the two cities is about200 kilometers.
   两座城市之间的距离大约是200公里。
2. 2. The distancebetween the two countries is over 1000 miles.
   两国之间的距离超过1000英里。
3. 3. The distance between thetwo points on the map is 50 meters.
   地图上两点之间的距离是50米。